1. Field of the Invention
The present invention relates to an electric actuator for transmitting the rotation of an electric motor as a drive source to a slide table for feeding a workpiece carried on the slide table.
2. Description of the Related Art
Electric actuators have heretofore been used to feed workpieces. One conventional electric actuator is shown in FIG. 16 of the accompanying drawings.
The conventional electric actuator, denoted at 2 in FIG. 16, basically comprises an electric motor 10 mounted on an actuator frame 20 and having a motor shaft 16, a drive force transmitting means such as a ball screw or feed screw 4 for converting a rotational drive force from the motor shaft 16 into a linear motion and transmitting the linear motion to another member, and a nut 6 displaceable in the axial direction of the ball screw to move a slide table (not shown) in the longitudinal direction of the actuator frame 20.
Between the electric motor 10 and the ball screw 4, there is disposed a coupling 30 which coaxially interconnects the motor shaft 16 and the ball screw 4 for transmitting the rotation of the motor shaft 16 to the ball screw 4. The ball screw 4 is rotatably supported at one end thereof by a support block 22 remote from the coupling 30. An encoder 12 is disposed in the vicinity of the electric motor 10 or integrally combined with the electric motor 10 for detecting a rotational speed or an angular displacement of the electric motor 10.
With the conventional electric actuator 2, the coupling 30 is required to connect the ball screw 4 and the motor shaft 16 coaxially to each other, and a plurality of bearings 24, 26, 34, 42 are required in a bearing block 8, a joint 18, a drive unit 14 to support the ball screw 4 and the motor shaft 16 coaxially with each other.
It is time-consuming and costly to assemble the above various components of the electric actuator 2. The coupling 30 takes up an extra space other than a range in which the slide table is movable in the longitudinal direction of the actuator frame 20. The space occupied by the coupling 30 imposes a limitation on the range of movement of the slide table such that the slide table cannot move the full longitudinal length of the actuator frame 20.